Cutting some shapes... with the help of water

The idea of cutting with thin jets of high-pressure water is not new – it was developed in the last century and is now used in many applications. “It is hard to imagine the effectiveness of a water jet as a cutting tool without actually seeing it in action,” said  Bob Hinchcliffe, technical director at Stelram Engineering. “Water jets can cut almost any material; with the addition of abrasive particles to the water, even stone and tough metals can be tackled with ease.”

While abrasives cannot be added to water to help cut food products, due to the issues of potential contamination, this is not a limitation of the technology, according to Hinchcliffe. “Any food that is so hard that it cannot be cut with jets of plain water is unlikely to find favour with consumers!” 

So, how do water jet cutters work and what are their benefits? The basic principle is simple. Essentially, a water jet cutter consists of a nozzle with a fine aperture, which is fed with high-pressure water from a pump. 

There is, of course, a bit more to it when it comes to making a practical cutter. The cutter needs to be able to withstand the very high pressures used – typically up to 4,100 bar. In addition, the nozzle that defines the water stream must be highly resistant to erosion so needs to be made from a very hard material such as ruby, sapphire or diamond. A high-pressure pump is also needed to supply the water to the cutter and the water must be softened because if it is too hard the dissolved solids can precipitate within the high-pressure parts of the pump.

Perhaps the most obvious benefit of water jet cutting is that there is no blade that needs to be sharpened and cleaned regularly. Indeed, as the pressurised cutting water is sterile, the risk of product contamination is eliminated. Another important benefit is that water jets cut very cleanly, without putting the product under pressure. This means that the product will not be distorted or damaged by the cutting process, Helping to minimise waste.

Water jets are also very controllable – 90º angles and corners can be easily achieved and, unlike laser cutting systems, they do not heat the product during cutting.

“Some companies have concerns about the water jet wetting the product. In practice, however, this is rarely a problem because the volume of water used is very small and it is moving at such a high velocity that it has little opportunity to produce significant wetting,” explained Hinchcliffe.

So, how can water jet cutting best be implemented in practice in the food sector? “A key factor to bear in mind is that, in almost every application, the water jet cutter will not be used alone – it will be just one component in a machine,” said Hinchcliffe. “At a minimum, the machine will need to place the product correctly and accurately for cutting, control the motion and operation of the cutter, and then remove the product from the cutting area. Depending on the complexity of the application and the degree of accuracy required, a range of technologies may be needed to complement the water-jet cutter itself.

“For example, if only modest cutting accuracy is needed and the machine operates at moderate speeds, it may be possible to control product positioning with ordinary photoelectric sensors. If, however, the highest possible accuracy is needed or if the machine is required to achieve very high throughput, a vision system may provide better and more consistent results,” continued Hinchcliffe.

Overall control for the machine that incorporates the cutter is almost certain to be handled by a PLC. In many cases this will need to connect to a factory network to allow communication with other production machines, as well as to cater for process monitoring and traceability requirements.

Western Mechanical Handling (WMH) has identified water-jet cutting as a growing trend in the food industry having seen a big increase in enquiries from food manufacturers for the for its use technology in production processes.  Drivers for its adoption are coming from three areas – the need for more control of the product, flexibility to cut random shapes and reducing costs.

WMH designs, manufactures and installs automated production solutions for the food industry. When developing water jet cutting solutions it advises that the cutting nozzle is mounted onto a servo drive and linked to a vision system to enable accurate product cutting without the need for touching and guiding the product, which can often be difficult, for baked food products in particular.  

The same vision and servo technology can be employed to plan the most efficient cutting pattern and carry out the cutting of random shapes – for example cutting different seasonal shapes.  

The final advantage of waterjet cutting over blade cutting is the cost saving in terms of product change-over, with no physical blade to be changed between products, production of different products can be almost seamless saving downtime and cleaning costs.  Similarly there are no parts to be swapped between product runs and there is no degradation of the cutting surface over time. 

To meet the growing interest in is this type of cutting technology WMH has built a test unit which has been put used for proving the principle of operation with a range of products including cheesecake, cream-slices, bread and vegetables.

Water-jet cutting has much to offer but it is often overlooked when specifications are being formulated for food industry projects. However, water is one of the strongest and most resilient elements on the planet –  it is able to carve its way through earth, metal and even rocks. So, next time you are thinking about the best way to trim, cut or slice a product, think water – it might just offer a good  solution.